Self-contained power actuator



March 23, 1954 B. N. ASHTON SELF-CONTAINED POWER ACTUATOR 4 Sheets-Sheet 1 Filed Aug 1, 1951 ET ICAL D OOF/E' NEW ii F I6. I. D/AME TRICAL GROOV n m J INVENTOR. BENJAMIN N. ASHTON u n A. all-2.

H IS ATTORNEYS.

B. N. ASHTON SELF-CONTAINED POWER ACTUATOR March 23, 1954 4 Sheets-Sheet 2 Filed Aug. 1, 1951 INVENTOR. BENJAMIN N. ASHTQN wdE H 15 ATTORNEYS.

B. N. ASHTON 2,672,731

4 Sheets-Sheet 3 Y m w SELF-CONTAINED POWER ACTUATOR March 23, 1954 Filed Aug. 1, 1951 V INVENTOR. BENJAMIN N. ASHTON BY WM EQKM HIS ATTORNEYS.

B. N. ASHTON SELF-CONTAINED POWER ACTUATOR March 23, 1954 Filed Aug. 1, 195i 4 Sheets-Sheet 4 n a x INVEKITOFEL BENJAMIN N. ASHTON IS ATTORNEYS.

Patented Mar. 23, 1954 2,672,731 SELF-CONTAINED POWER ACTUATOR Benjamin N. Ashton,

Kingston, N. Y., assignor to Electrol Incorporated, Kingston, N. Y., a corporation of Delaware Application August 1, 1951, Serial No. 239,801

8 Claims.

This invention relates to improvements in self contained electro-hydraulic actuators or jacks to actuate landing gear, wing flaps and other movable elements of aircraft and other devices. The invention further relates to an improved electrically and hydraulically actuated jack or power actuator and to an improved type of selec tor valve. It also relates to a system for actuating a selector valve for devices of the type re ferred to above and other flow control systems.

Devices of the type embodying the present invention comprise a unitary self-contained hydraulic power unit including a pump driven by an electric motor to supply liquid under pressure to a jack carried by the supporting structure for the motor and the pump, and a selector valve system also mounted in the supporting structure for controlling the supply of liquid to the jack to drive it in either direction, selectively. More particularly, a typical power actuator includes a casing having a reservoir therein to receive liquid and a pump mounted in the casing and communicating with the reservoir to withdraw liquid therefrom and supply it under the control of a selector valve to a jack or ram also mounted on the casing. The pump is driven by an electric motor also carried by the casing and the motor is controlled by means of suitable switches in the cockpit or other convenient location in a vehicle or aircraft and by limit switches to thereby start and stop the motor, as may be required, to drive or stop the jack.

The selector valve mechanism is electrically controlled to admit liquid from the pump into the jack and to drive it selectively, in either direction of operation. The selector valve involves a novel control system wherein the individual valves making up the selector valve are actuated by means of liquid under pressure under the control of solenoid actuated valves operable from a remote point. The individual selector valves are of the pressure balanced type, and are opened by means of unbalancing pressures supplied by the pump under the control of the solenoid valves to assure positive operation of these valves. The use of the pressure in the system to open and close the selector valves makes possible a considerable simplification of the system for controlling these valves and eliminates mechanical actuating elements, such as cams, cranks, or the like, which are commonly used in such selector valves.

Systems of the type embodying the present invention can be positioned from a main control point and can be readily at places remote controlled by switches conveniently located on a control panel at the control point. Inasmuch as each actuator unit is self-contained, the only connections required are the electrical connections between the switches and the units which can be installed easily in a minimum of space.

For a better understanding of the present invention, reference may be had to the accompanying drawings, in which:

Fig. 1 is a diagrammatic illustration of a typical system, including selector valves, a jack and pump, embodying the present invention;

Fig. 2 is a view in side elevation of a typical power actuator of the type embodying the present invention;

Fig. 3 is a view in vertical section through the power actuator shown in Fig. 2, with the motor removed;

Fig. 4 is a view in end elevation of the power actuator illustrated in Figs. 2 and 3;

Fig. 5 is a view in section taken on line 5-5 of Fig. 3;

Fig. 6 is a view in of Fig. 3;

Fig. 7 is a view in end elevation of the power actuator looking toward the left-hand end of Fig. 2;

Fig. 8 is a bottom view of the actuator; and

Fig. 9 is a wiring diagram of the system.

The system illustrated diagrammatically in Fig. 1 of the drawing shows the general principles underlying the construction and operation of power actuators of the type embodying the present invention. As shown in Fig. l, the system includes a reservoir I0 to receive liquid, and a pump H, such as a gear pump, mounted in the reservoir to Withdraw liquid therefrom and supply it to a pair of solenoid-controlled valves I2 and i3 through a conduit I4 having the branches [5 and I 6 connected to the liquid-receiving chambers l2c and I341. of the valves I2 and I3.

The conduits I5 and it also communicate with the poppet valves ll and Ill respectively, which control the flow of liquid to the hydraulic jack or motor l9. The valve I1 is connected by means of a conduit 20 to the left-hand end of the cylinder and the valve I8 is connected by a conduit 2! to the right-hand end of the cylinder. The conduit 2c is also connected by means of a return conduit 22 to a return poppet valve 23 and to a thermal relief check valve 24. Similarly, the conduit 2| is connected by means of a return conduit 25 to a return poppet valve 26 and a thermal relief check valve 21.

The return poppet valves 23 and. 26 are consection taken on line 6-6 3 nected by return conduits 28 and 29 to the reservoir In, these conduits also communicating with the thermal relief valves 24 and 21 so that excess, heat-expanded liquid can be returned to the reservoir.

The solenoid control valves I2 and iii are alike. The v'alveiZ, for example includes a'solenoid coil 3fiwhich, upon energiza'tion, displaces an armature 3i engaging at its outer end a slide valve plug 32. The slide valve plug passage 33 therein and a diametricallyextending groove 33b in its end through which liquid from the conduit 15, for example, can flow upwardly and through the lateral port 33a into a passage 34 communicating with the back of the poppets 35 and 38 of the valves I! and 2t. Thegroove 33?) provides a flow passage even when the end of the armature 3i engages the end of the valve plug 32.

The solenoid valve i3 is similarly connected to the'backs or the poppet valves 13 and 23 by means of a passage and chamber system 31.

The passage 32 is connected by means of a restricted orifice'til to the return line'28 and the passage 37 isconnected by means of a restricted orifice'39 to the return conduit 28.

The slide valves l2 and 83 when tie-energized, prevent communication between the passages l5 an'd3fl'andthe passages l6 and 37.

The poppet valves i? and it are oi substantially the same construction andare of the pressure" balanced type. As best shown in Figs. 1, 5 and 6, the poppet valve plug 35 has a valve head 40 having an area exposed to the pressure of the liquid equal to the area of a. balancing pistons! on the opposite'end of the valve stem 42. The valves 23 and 25 are similar to the'valve 11' but they are normally urged shut by means of biasing v springs 43' and M.-

Referrlng' again to'Fig. l, and assuming that the pumpii is in operation, and the solenoid control valves i2 and liia're closed, liquidunder pressure is supplied through the conduit It: to each or the valves El and it between the rod endsof the'valvehead lfiandthe piston l i. liquid circulated by the pump is returned tothe resrvoir'by meansof the main relief or unloading valve 45" interposed between the conduit I'd and the reservoir it. The pressure in the conduit 3 is about the same as the pressure or the liquidat the intake of the puinp H- soth'at the pressure'ohthe'rod endof the piston M will be' greater than the pressure onits head end.

when, for example, the solenoid of the solenoid valve i2 is energized, the valve plug- 32 is displaced downwardly and the liquid from" the pump flows through the passage 33 and the the groove 33b in the plug and the portlita into the passage 34 behind the pistons of the'valves W and 26. The liquid pressure acting on the head end of the piston M then becomes equal to the pressure on its rod end.

Liquid cannot flow from the valve ii through the conduit 22' because it is opposed by the biased thermal relief check valve 2 3 and the retur poppet valve 23 w ch is biased closed and further is in a balanced condition. Liquid from the right-hand endof the cylinder can, however, flow through the conduits 2| and 25, through the return poppet valve 23 when it is open and the conduit 29 back to the reservoir Hi.

When the solenoid valve l2 closes, communicatioh between the conduit 1-5 and the assage 34 is cut ofi. As the liquid in the passage 34- bleds offthrough the orifice 38 into the reservoir has an axial 'eannot'flow from the motor 49' to l0 (low pressure zone), the pressure in the passage 34 drops to pump intake pressure, and the pressure on the rod end of the piston 4| becomes greater than the pressure on its head end and the unbalanced piston will tend to urge the valve plug 35 to closed position. The return poppet 26 will also be urged to closed position by the spring 43- a'nd theuhequa'lpressures onthe'piston and valve head of the valve 26. Inasmuch as the valve 26 is closed, the liquid to the right of the piston lt istrapped and the piston 46 cannot move to the right, even if the valve ll remains open.

The operauorior the system is as follows:

Assume the-system is in the condition shown in- Figure 1 with all-of the valves, l1, I8, 23 and 26, closed. The pump II is operating so that pump output (high) pressure is present in lines l4, l5 and'lfi. The return lines 28 and 29 and the lines 34 and 3l-are at pump intake (low) pressure.

The system is full ofliquid and the liquid pressure in rhotor I!) on both sides of the piston 48 therein isequaltopumpoutlet (high) pressure.

With the conditions set acting on therod ends of the piston 4i and the valve'plug 4B of the valve I1 is the same and there is no tendency for the valve to be opened by the pressure between the piston H and the valve'plug 4t. The'pres'sure-acting'onthe head end of the valve plug &3 is the same as on its rod end because the motor 1 9 and the line's20 and 22 are'at pumpoutletpressure- However, the preSSLlIeOn the head end of the piston is pump intake (low) pressure, much below the pumpoutlet (high) pressure; so that the force acting on the head end ofthe valve plug 40 ismuch greater than the force acting on the head end of the'piston M. This unbalance of forces causes the valve IT to remain-closed.

When' the solenoid valve l2 is'energized, the pressure in the line 34- becomes equal to the pressure in the line l5;

The valve head of the valve 28 is subjected at its head end to" the low pump intake pressure and at its rod end to the high pump outlet pressure (systempressure). The rod and head ends ofthe'pistonare subjected topump-outlet pressure. Accordingly,- the valve will be unbalanced and willopen, thereby allowing liquid to flow to the intake of the pump-from the right hand end of the motor l9, producing a'reduced pressure in the righthand end of the cylinder of the'motor l9 and allowing the piston let/herein to move to the right. resulting from moveme t of the piston 46 will reduce the pressure exerted on the head endof the valve head 40 to less than the pressure on the head end of the p-iston M so that-the valve plug 35 becomes unbalanced and opens. With both of the valves lT-and 26" open, the piston 46 will continue to move trated inFi'gure'l. Reduction of pressure in the line 34 and on the headend' ofthe piston of the valve 2-6 allows this valve to close so that liquid the intake of the pump ll". Inasmuchasthe valve l? is open, the system is loaded to pump outlet pressure. The conditions now being the same as those initially described and present,- the valve plug as Will be unbalanced, Wm clbse amine system'- forth above, the force The reduced pressure to the right until it reaches the end of the cylinder or until the valve may now be had to will be restored to a condition in which both of the valves 26 and H are in a closed position.

To move the piston 36 in the opposite direction, the solenoid valve I3 is energized so that the poppets I 8 and 23 are opened and liquid flows through the valve It into the right-hand end of the cylinder is and out of the left-hand end of the cylinder through the valve 23 to the reservoir Ill.

Due to the pressure balanced condition of the selector valves, little energy is required to actuate them and as a consequence the system is easily and positively operated to control the jack I9.

Having described the general principles of operation of a typical system and unit, reference Figs. 2 to 8 of the drawings showing a typical power actuator unit.

The unit includes a casing member 513 which,

as shown in Figs. 5, 6 o.nd '7, has a semicircular upper end portion 55 and a generally rectangular body portion 52. The reservoir H3 is formed in the upper semicircular end of the casing and may be of cylindrical shape, as shown in Figs. and 6. Pump l l is mounted within the reservoir with its drive shaft 53 connected to an electric motor 54 which is supported at one end on the casing 50. The left-hand end of the reservoir Iii, as shown in Fig. 3 is closed by means of a cover plate 55 carrying an eye lug 56 by means of which the unit can be supported in the aircraft or other structure. The cover plate 55 is secured by means of screws 5i, or in any other way, to the left-hand end of the casing 5d. The cover plate includes a filling opening 58 communicating with the reservoir ill and receiving a plug 59 to enable the reservoir Ill to be drained and refilled as required. If desired the reservoir may be pressurized through an air check valve in the plug 59.

Directly below the motor 54 and supported at its left-hand end in the casing Ell, is the jack is. The jack may consist of a. tubular member til having a threaded left-hand end BI screwed into a threaded circular recess 62 in the lower rectangular part 52 of the casing 59.

The piston 46 includes acylindrical head 63 mounted on a tubular or solid piston rod 84 which extends through an annular closure cap 65 mounted on the right-hand end of the tubular member 60. Suitable liquid-tight seals are interposed between the closure and the tubular sleeve 60 and between the closure and the piston rod 5 3 to prevent leakage.

The selector valves including the poppets ll, I8, 23 and Eli are mounted in the lower section 52 of the casing behind the cylinder l9 and with the axes of the valve plugs generally perpendicular to the axis of the cylinder it. Referring to Figs. 3 and 5, it will be seen that the valves I! and 26 are mounted substantially one above the other in parallel bores 6t and ill extending inwardly from the left-hand edge of the casing as viewed in Fig. 5. The outer ends of these bores are plugged by means of suitable threaded plugs and caps 55a and 67a. The plugs Elia and did act to limit the opening movement of the valve plugs of the valves I? and 26 so that the balancing pistons thereon do not block the passages I5 and 25, respectively. The valves it and 23 are mounted in the parallel bores 68 and 68 which are spaced apart generally vertically in the casing (Figs. 3 and 6). These bores have their outer ends closed by the plugs 88a and 69a.

The solenoid control valve I2 for controlling the valves I I and 26 is mounted below the'valve I! in a bore Ill extending from the right-hand side of the casing as viewed in Fig. 5. The coil of this valve has a threaded casing 3% which is screw in the bore It. Above the solenoid valve 70 in the bores II and 72, respectively, are the main relief valve and the thermal relief valve 21 which are of the ball check type and are retained in the bores by the threaded plugs Ila and 72a.

As shown in Fig. 6, the solenoid control valve I3 is mounted in a bore 73 extending inwardly from the right-hand end of the casing and terminating about mid-way between and communicating with the bores 68 and Gil.

The thermal relief valve 24 is mounted in of the threaded plug 14a.

The connections between the several elements referred to above are as follows. The cover plate is provided with a passage 15 which communicates with a conduit or pipe I6 connected to the outlet of the pump II so that the liquid under pressure is delivered through the passage. The passage I5 and pipe I 5 correspond to the conduit I 4 in Fig. 1. The passage 15, at its lower end, communicates with a cross bore 71 corresponding to the passage I5 (Fig. 1) which introduces liquid under pressure into the poppet valve I 7 between the head 40 and the piston 4I thereof as shown in Fig. 5. The passage 11 also intersects a reduced portion of the bore 10 in which the slide valve plug 32 is receivedso that liquid can flow through the passage 33 therein and the port 38a into the passage 34 behind the valves I! and 25. tion in Fig. 3 may the bottoms of the The chamber or be formed by recess milling bores and 61.

space 18 in front of the plug head 46 formed by the bore 66 and a closure plug 66a communicates with a passage 88, Figs. 3, 5 and 6 connected to the left-hand end of the cylinder I9 as viewed in Fig. 8. This latter passage corresponds to the passage 28 shown in Fig. 1. The connection corresponding to the passage 22 between the valve I7 and the valves 23 and 24 of Fig. 1 includes the passage 8|, Figs. 3 and 6, between the left-hand end of the cylinder I9 and the space between the plug head and balancing piston of the valve 23, and the passage 95 between the left-hand end of the cylinder I9 and the bottom of relief valve 24.

The connections between the valves I8 and 26 and the right-hand end of the cylinder are as follows.

The cylinder end closure 65 is provided with a passage and port 82 communicating with the interior of the cylinder and with a pipe or conduit 83 which is connected to a passage or bore 84 in the casing 56 above the solenoid valve l3 as shown in Figs. 5 and 6. The bore 84 and the conduit 83 correspond to the passages 2| and 25 of Fig. 1.

The pressure passage communicates with a transverse passage 85, Figs. 3 and 6, which communicates with the reduced portion 13a of the bore 73 in which the solenoid valve I 3 is mounted. Passage 85 corresponds to passage lb of Fig. 1. As indicated above, the bore 73 intersects and communicates with the bores 68 and 59 in which the valves I8 and 23 are mounted so that liquid under pressure is supplied against the inner end of the slide valve plug 86 of the solenoid valve I 3 and also to the zone between the ends of The passage 34 shown. in secaware 1;:

the =p1ug=of the valve i8. The solenoidivalve 13;:

67L containing the return poppet valve 25 to.

supply liquid to the space between the headand 7 piston of the valve. The-bore Bibyrecessmilling int'ers'ects a passage 88 which,- inturn, inter- '84 connected to the. right-hand sects passage end 'of the cylinder. The pressure exerted between the ends of the poppet valve 26' has no efiect on it: inasmuch as this valve isxbalaneed andis further biased-to closed-position by the spring 43.

The chamber 9!] in front of the valve 23 is connected to the reservoir in by means of areturnzpassage 91' corresponding to the passagez28 of Eig. 1. Similarly, the chamber 92. infront of the valve :26 is connected to thereservoir l bywa returntpassage' 93 1 corresponding. to: passage 2950f Fig.1;v

The: pressure chamber 34 behind the valves li and. 26 is conneotedLthrough the orifice plate 38 (0rifice 3'8) Fig. 3, to the reservoir l0 zand the passage. 31 isiconnected by the orificeplate 39. (orifice SQ) Fig. 3, tothe reservoir m.

The" thermalrelief valve. Nisinterposed betweena' bore 95, Figs. 3, 6 and 3, connected to the left-handrendofthe cylinder ltianda communicating bore 96 which connects with a verticall'passa'ge 9-1 in the end plate 55 in: communication with the reservoir Hi.

The main reliefv valve 45: is connected by a passage 8.5 an'd a'passage 98ito the reservoir H); as shown in Fig. .5. The thermal relief valve 21'! is interposed. between the passage 99. and: the passageu98- .As shown'in Fig. 5,,thepassage 98 intersects thebore 12in which the reliefvalve .zlris'mounte'd atz' the' downstream. side of. the valve 21.

Thevarious connections describedabove .in the typicalembodimentcorrespond to the connections'shown. in Fig. 1. and: the unit is operated in; the manner described in connection with Fig.1;

In". order'to limit the travel ofv the piston, a

pair'of'a limit. switches wlland Isl are mounted. bracket cs2. carried by the end in 1. a casing or closure 65*for the'cylinden The limit: switches are normally biased to closed position. The switch Hi1!v has an outwardly extending switch button H13 which is engaged by a disc-lik collar- [0T4 mounted near the outer end of thepiston rodi ii i" to open the switch at thev inner limit ofmovement of the piston and piston rod.

The limit switch: it! is actuated by. means of a push rod I65 which is slidably mounted in a bore H36: in theclosure 65 and isnormally urged inwardly by means of a spring Mil engaging a flange 108 on the push rod and a closure collar I09 threaded in the outer end of the bore m6. Thus, when the'right-hand face ot the piston 63. strikes the inner end of the push red, the switch I M 'isropened.

The electrical circuit forthe system. is shown source of 'elec-' in-Fig. 9. The:circuit.includes a tnioal' energy such as a battery i-i-ii andhaving one. pole thereof connected to one terminal of each: of the coils of the. solenoid valves l2 andv 54a of the motor 54 .v

I3 and to: one terminal The other terminal. or th v battery is connected -mi11ing 1 the inner;

The liquid inthe bore.

- connected through the toia. double pole; doublethrow switch. (H; one blade I 1| 2 of fwhichccooperates with the contacts:

tactv H4 is connected through the limit switch. 54b of the motor 54; The.

I'M to :the terminal contact H6 is connected to the coil of the solenoid switch l3.and'the contact ll'l isconneoted to'the end of the coil of the solenoid switch 1 12.

When the piston rod 64- is fully projected, the;

switch; I01 is openas illuStratedJinFig'Q. Ifthe blades H2 and H5 contacts H3and Ht, the solenoid valv l3 and thermotor 54 are energized and the piston begins. to. move to the left until the collar I04 on the the switch button I 03 opening piston rod strikes the switch I09: thereby de-energizing M sothat the pump stops.

the motor piston. reaches time; ofx'course, the switch double throw switchis-movedto engage th contacts H4 and H1, the-solenoidvalve l2 and the motor" 54 are energized and the latter-operates until the switch HM is opened by engagement of the piston with the push rod I05 unless the switch H! is opened or its position. reversedbefore. the piston rod is fully extended. Upon opening the double throw-switch Hi both of the solenoids and the motor are de-energized and no movement of the pistoncan takeplaoe because of the liquid trapped in the cylinder.

While theselector valve system has been-described with reference to its use in a self-contained electrically will-'beunderstood that it may be-usedequally. well in other hydraulic or liquid flow control systems. It will beunderstood also, that thegeneral arrangement of the elements of thehydraulie actuator may 'be .modifiedto; conform to the conditions'under which parting from the invention. Therefore; theyembodiment of the invention described herein should" be considered as illustrative andnotas.

turnport and normally maintained in a closed. position to prevent discharge of liquidlfrom said and a third normallyclosedmotor to said pump, valve interposed between saidpressure'port and said first/and second valves, said thirdvalve being movable to open positionto'apply fluid pressure tosaid' first and second valves to openthemand actuate said motor.

2. Thehydraulic actuator setforth in claim .1, said first. and second valves comprises: a cylindrical: chamber, a seattherein.

in which each of interposed vbetween said Pump. andrsaid. motor,. a

The contact I I3 is are then engaged with the The m0tor-can.b.estopped by opening the switch H1. before the its'limit position. In the mean-- l M 'hasclosed because oftmovementaofthelpiston and piston rod. Ifthe:

actuated hydraulic system, it

it is used and thatitmay be made in various sizesand forms without-dd a return port poppet head cooperating with said seat, a stem extending from said head along said chamber, a balancing piston on said stem having an inner face subjected to the pressure of the liquid acting on opposed face of said poppet head, and a port in said chamber adjacent the outer face of said piston and connected to said third valve to supply liquid pressure against the outer face of said piston.

3. The hydraulic actuator set forth in claim 1 comprising a second separate set of said first and second valves interposed between said pump return port and said discharge port and said pump pressure port and said motor inlet port, respectively, and a separate said third valve interposed between said second set of valves and said pump pressure port to supply liquid pressure to said second set of valves to open them.

4. A hydraulic actuator comprising a hydraulic motor having an inlet port to receive liquid and an outlet port to discharge liquid, a motor-driven pump to supply liquid under pressure to said motor, said pump having a pressure port and a return port connected to said inlet port and said outlet port, respectively, a first pressure balanced poppet valve interposed between said pressure port and inlet port and normally maintained in closed position to prevent flow of liquid to said inlet port, a second pressure balanced valve interposed between said outlet port and said return port, and normally urged to closed position to prevent flow of liquid from said outlet port to said return port, said first and second valves each having a, poppet valve head and a balancing piston having inner opposed faces exposed to the pressure of the liquid, a separate connection between said pressure port and the first and second valves to supply liquid under pressure against the outer faces of said pistons to urge said first and second valves to open position, a third valve interposed in said connection to open and close said connection, and means including a restricted orifice connecting said separate connection to said return port to relieve said outer faces of said pistons from liquid pressure in said separate connection to allow the first and second valves to close.

5. The hydraulic actuator set forth in claim 4 in which said third valve comprises a slide valve normally biased to closed position, and electrically actuated means for moving said slide valve to open position.

6. In a hydraulic actuator, the combination of easing having a reservoir for liquid therein, a hydraulic jack including a cylinder having ports at its opposite ends and a piston reciprocable in said cylinder, said jack being mounted on said casing, a pump mounted in said casing and having an intake passage communicating with said reservoir, a motor mounted on said casing to drive said pump, and a control valve system in said casing to selectively supply liquid to either port of said cylinder and discharge liquid from the opposite end of said cylinder to said reservoir, said control valve system comprising separate pressure balanced valves interposed between said pump and each port of said cylinder, separate pressure balanced valves interposed between each port and said reservoir, each of said valves normally being urged to closed position, and a pair of separate control valves to supply pressure, one being connected to one pressure-balanced valve between a cylinder port and the pump and to one valve between a cylinder port at the opposite end of the cylinder and the reservoir, and

10 the other control valve being connected to the others of said separate valves to supply pressure from said pump to unbalance the valves selectively and supply liquid under pressure to displace said piston.

7. In a hydraulic actuator, the combination of casing having a reservoir for liquid therein, a hydraulic jack including a cylinder having ports at its opposite ends and a piston reciprocable in said cylinder, said jack being mounted on said casing, a pump mounted in said casing and having an intake passage communicating with said reservoir, a motor mounted on said casing to drive said pump, and a control valve system in said casing to selectively supply liquid to either port of said cylinder and discharge liquid from the opposite end of said cylinder to said reservoir, said control valve system comprising first separate passages connecting said pump to the ports at opposite ends of said cylinder, second separate passages connecting said reservoir to said ports, separate pressure balanced valves interposed in said passages to prevent and permit flow of liquid therethrough, said valves normally being closed to prevent flow of liquid, additional passages communicating with said valves to supply liquid from said pump to unbalance and open said valves, a first control valve interposed in one of said additional passages to open and close said one additional passage to supply liquid under pressure to actuate a valve in one of said first passages and a valve in one of said second passages, and a second control valve interposed in the other additional passage to open and close the latter to actuate a valve in each of the other first and second passages.

8. In a hydraulic actuator the combination of casing having a reservoir for liquid therein, a hydraulic jack including a cylinder having ports at its opposite ends and a piston reciprocable in said cylinder, said jack being mounted on said casing, a pump mounted in said casing and having an intake passage communicating with said reservoir, a motor mounted on said casing to drive said pump, and a control valve system in said casing to selectively supply liquid to either port of said cylinder and discharge liquid from the opposite end of said cylinder to said reservoir, said control valve system comprising means including two separate pairs of pressure actuated valves to admit liquid from said pump to either end of said cylinder and discharge liquid from either end of said cylinder to said reservoir, said pressure actuated valves normally being biased to closed position by pressure of liquid therein to prevent movement of said piston, and means including a separate pair of control valves, each corresponding to and connected to separate pressure actuated valves for admitting liquid to said jack and. for discharging liquid from said jack to supply liquid under pressure from said pump to actuate corresponding pressure actuated valves and open them to drive said piston in either direction.

BENJAMIN N. ASHTON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 412,327 Gibson Oct. 8, 1889 1,910,766 Hobson May 23, 1933 1,927,700 Dickinson Sept. 19, 1933 2,275,963 Herman et a1. Mar. 10;, 1942 

